Polishing element



June 1945. R. M. HILL 2,378,630

POLISHING ELEMENT Filed Nov. 16, 1943 FIG.

RALPH M. HILL Patented June 19, 1945 POLISHING ELEMENT Ralph M. Hill, Lancaster Township, Lancaster County, Pa., assignor to Armstrong Cork Company, Lancaster, Pa., a corporation of Pennsylvania Application November 16, 1943, Serial No. 510,461

7 Claims.

This invention relates to polishing elements and more particularly to an element for polishing silver and the like with abrasive particles and oil or water. The element preferably takes the form of a wheel which may be mounted for rotation and the abrasive particles and oil or water are applied to the wheel or to the piece to be polished or to both.

Common practice has been to use wheels formed generally of a single thickness of walrus hide, held as a wheel by a suitable central fastening device. Walrus hide performs very well in the polishing of metals of the hardness of silver and this particularly fine polishing efiect is believed to be due in part at least to the ability of the walrus hide to absorb oil and hold the abrasive particles, thus permitting relatively rapid polishing and at the same time some burnishing effect is undoubtedly obtained from the contact of the walrus hide itself with the metal under treatment. Due to the advent of war and other conditions, however, the available supply of walrus hides has become limited.

An object of my invention is to provide a polishing element which may be formed from an artificial mass which will have the effect of polishing silver and the like in much the same manner as the walrus hide wheels now in use and which will produce the same high quality finish as rapidly as now possible with walrus hide.

An element which performs substantially as well as the walrus hide wheels has been prepared using a matrix of an oil-resistant synthetic polymerization product of an open chain aliphatic conjugated diene and incorporating into this matrix a relatively large volume of cork granules. (Generally, the piece to be polished is first subjected to the action of the wheel with abrasive particles and water to perform the rough polishing. This is followed with a similar polishing action using finer abrasive particles and oil. Thus the matrix must be resistant to both oil and water.) The cork granules have been found to give a burnishing action similar to that obtained with walrus hide. In order that the Wheel or element will hold the abrasive and the oil so that the same may be available at the working surface, the matrix is provided with a myriad of small, relatively uniformly spaced openings. This is obtained by providing an agent in the mix which is effective for sponging the matrix. The pores may, of course, be otherwise formed but by the use of a blowing agent, desirable, relatively small, uniformly spaced openings are provided. The element is preferably formed in a mold and heat and pressure applied to efiect vulcanization. The mass is then removed from the mold and a working surface is formed by severing the body to the desired shape. This may be accomplished by removing the outer skin surface in the event the element is molded as a wheel. This exposes the cork granules at the surface, the same being imbedded in and held by the matrix. Also, it makes available the porous interior structure of the matrix.

Where the element is to be used for relatively high speed operation, it is desirable to incorporate fibers or similar reinforcing strands into the mass. Good results have been obtained when cotton fibers such as curtain shearings are used for this purpose.

In order that my invention may be more readily understood, I will describe the same in connection with the attached drawing in which:

Figure 1 is a sectional view showing a. polishing element in the form of a wheel mounted on a typical support, and

Figure 2 is a view partly in section and partly elevation showing a polishing element of block form, with a surface portion enlarged to better illustrate the structure.

The polishing wheel of Figure 1 is generally indicated by the numeral 2 and includes a matrix 3 carrying fibers 4 and cork particles or granules 5. The small voids or openings in the matrix are indicated at 6. It is difiicult to show the precise structure of the element because the openings are relatively small and are numerous, many being present in each square inch of the working surface. The cork particles and fiber particles are heterogeneously distributed throughout the ma trix and upon an examination of the severed working surface, their presence is noticeable in such volume that they appear to constitute a major portion of it, being separated by thin walls of the matrix forming material and in thi matrix are found the open ended cells which receive and hold the oil and abrasive. The matrix is relatively soft and resilient and thus holds the cork granules in spaced relationship but capable of limited fiexure. These cork granules serve as burnishing elements and they must be well anchored in the body to prevent their disengagement under operating conditions. As the element i compressed, the abrasive is brought into the engagement with the surface to be polished and a combination of abrading and burnishing is eifected in much the same manner as occurs with the walrus hide wheels.

The element 2 is mounted upon a spindle 1 by means of a locking screw 8. Any suitable supporting arrangement may be provided. For some services a pad of polishing material is all that is required. A pad of this sort is shown in Figure 2. It includes a matrix 9 having severed cork granules l disposed at the working surface. An attempt has been made in Figure 2 by exaggeration to show the severed cells I l in the matrix 9. Where a hand polishing element is desired, it is not always necessary to incorporate the fibers.

The polishing element may be formed of a composition such as the following, all parts being given by weight:

Neoprene (chloro-2- butadiene 1,3) s 100 30-50 mesh cork 25 Curtain shearings 25 (Burnishing agent) (Fibrous cotton reinforcing filler) Di-ortho-tolylguanidine. 1 (Plasticizer) Mineral oil 20 (Softener) P-25 cumar 3 (Softener) Light magnesium oxide. 4 Bicarbonate of soda.. Steariqacid 5 Kalite #1 Titanium dioxide- Total 216 As pointed out above, the essential ingredients of the composition are the polymerization product of an open chain aliphatic conjugated diene, cork, and fibers. The other compounding ingredients are conventional in synthetic rubber mixes and may be substituted freely in the usual manner to obtain the desired physical properties in the flnished product.

In place of neoprene as the polymerization product of an Open chain aliphatic conjugated diene, other polymerization products of conjugated dienes may be used provided they are resistent to deterioration under operating conditions where oil is present and are sufficiently water-resistant to withstand use where water is used in the polishing instead of oil. Polymerization products of butadiene and acrylonitrile sold under the designation Hycar, Chemigum, or Buna N may be used. Also, polymerization products of isoprene and acrylonitrile may be used. The polymerization product of butadiene and styrene is not satisfactory for the reason that the material lacks oil resistance. Natural rubber is unsatisfactory for the same reason.

In place of curtain shearings other fibrous materials may be used such as wool fibers, flax, or synthetic fibers of rayon or nylon or the like. In fact, any fibrous material which will reinforce the matrix may be used. The amount of cork incorporated into the matrix may be varied to a limited extent depending upon the type of work to be polished and also upon the type of element to be produced. For example, where a polishing wheel is made, it is possible to use a lesser amount of cork particles than in a hand polishing element. Because of the speed of the rotation of the wheel, an adequate burnishing effect may be obtained with less cork. In the above example, a major portion of cork by volume is incorporated. The amount of neoprene or other polymerization product which constitutes the binder may likewise be varied over a lesser range, depending upon the amount and size of cork granules incorporated.

The fiber content may also be varied. Here again, considerable leeway is possible, depending upon the service to-which the element may be put, and as pointed out where the element is used as a hand polishing element, the fiber may be omitted entirely.

Generally, for a polishing wheel to replace walrus hide, the proportioning should be Within the following limits using 100 parts by weight of neoprene:

Parts by weight Cork 10 to 50 Fiber 15 to The particular size of cork particles used preferably falls within the range of 10 to 200 mesh. Particularly good results are obtained with 30 to mesh cork but 20 to 30 mesh cork also gives good results and for certain flne polishing, cork of 50 to 200 mesh serves very well.

The mass is compounded in the usual manner of forming synthetic rubber compounds, the blowing agent and cork being added last on the mill. If a wheel is to be formed, the milled mass is placed in a mold and heat at about 300 F. is applied for about 45 minutes to effect blowing and curing. for a wheel about three-fourths of an inch in thickness. The temperature or time of curing will depend upon the type of binder employed, thickness of the wheel or mat, hardness required and other variable factors with which the skilled compounder is familiar. Since the polishing element should be resilient and compressible (this resilience is enhanced by sponging the matrix, the bicarbonate of soda in the above example being a sponging agent activated by the stearic acid) the mass is not compressed to any substantial degree during molding and the compound is not vulcanized to a hard consistency. Exceptionally good results have been obtained with polishing wheels having a specific gravity between .64 and .68. In all events, the specific gravity should be in the neighborhood of this range, say between .50 and 1.00 for best results in polishing wheels. For hand polishing, the density is not so important but the element should possess sufficient resiliency and compressibility to permit the cork granules to effect the burnishing action and to likewise permit the abrasive particles to be resiliently urged against the surface under treatment. The cells are so numerous that when they are filled with abrasive particles and oil or water, they present with the cork granules a substantially continuous polishing and burnishing surface.

After molding, the articles are cut to expose the cork granules and to provide the open ended cells for the reception of the oil and abrasive. In polishing wheels this is preferably obtained by mounting the wheel and grinding the working surface to remove at least the outer skin.

In polishing blocks or pads, the mass may be formed into a mat which is cut into pieces of the desired size and shape, the working surface being formed by one of the cut surfaces of the block. Here too, the surface may be formed by grinding to produce a uniform surface.

While I have illustrated and described a preferred embodiment of my invention, the same is not limited thereto but may be otherwise embodied and practiced within the scope of the following claims.

I claim:

1. An element for polishing silver and the lik with a mixture of abrasive particles and oil comprising a compressible cellular matrix of an oilresistant vulcanized synthetic polymerization product of an open chain'aliphatic conjugated diene and cork granules distributed throughout said matrix in spaced relationship, the working surface of said element being constituted of ex-- posed cork granules, separated by the cellular matrix, the cells of which are small and closely spaced to receive and hold the abrasive and oil during polishing.

2. An element for polishing silver and the like with abrasive particles and oil comprising an artifici'al mass having a working surface constituted of spaced cork granules to effect a burnishing action, fibers to reinforce the mass, and a compressible cellular matrix of an oil-resistant vulto effect a burnishing action, fibers to reinforce the mass, and a compressible cellular matrix of an oil-resistant vulcanized synthetic polmerization product of butadiene 1,3 holding the cork granules in spaced relationship, with the matrix between the spaced granules having small-sized cells open at the surface to hold the abrasive and oilused-in polishinl.

5. An element in accordance with claim 4 in which the oil-resistant vulcanized synthetic polymerization product is chloro-z-butadiene 1,3.

6. An element for polishing silver and the like with a mixture of abrasive particles and oil comprising a compressible cellular matrix including 100 parts by weight of an oil-resistant vulcanized synthetic polymerization product of an open chain aliphatic conjugated diene, 10 to parts by weight of cork granules uniformly distributed throughout said matrix in spaced relationship, and 15 to 40 parts by weight of a reinforcing fiber heterogeneously interspersed throughout the matrix, the working surface of said element being formed of exposed severed cork granules, fibers, and open ended cells of the matrix, the cells being smalland closely spaced to receive and hold the abrasive during polishing, a substantial portion of the workingsurface being constituted of burnishing elements.

7. An element for polishing silver and the like with abrasive particles and oil comprising an artificial mass-having a working surface constituted of'spaced cork granules of a size within the range of about 10 to 200 mesh, fibers reinforcing the mass, and a compressible cellular matrix of an oil-resistant vulcanized synthetic olymerization product of an open chain aliphatic conjugated diene holding the cork granules in spaced relationship, with the matrix between said spaced granules having a myriad of smallsized cells which will hold the abrasive and oil during polishing.

RALPH M. HILL. 

